The present invention relates generally to pulse radars, and particularly to a pulse radar which utilizes the fact that the coherent phase of an intermediate frequency of a return signal shifts with the speed of an object moving relative to a given point. More particularly, the invention relates to a noise-immune circuit for processing the intermediate frequency signal to determine the relative speed of the moving object.
A prior art processing circuit for pulse radars utilizing the phase shift of the intermediate frequency signal determines the phase shift of the intermediate frequency signal by comparing its amplitude with a set of fixed threshold levels. However, the amplitude of the intermediate frequency signal fluctuates because of the presence of noise and as a result, the processing circuit generates a false output. This is particularly severe when the relative speed of the moving object is low, since the peak value of the intermediate frequency signal tends to dwell on a level near the threshold levels.